Optical data storage is a known form of data storage. Known optical storage media such as compact disks, CD-ROMs, and DVDs are two-dimensional media storing separate bits of information in separate small areas on one or more surfaces. Although these optical data storage media have the capacity to store large amounts of information, there is an ever-increasing need to increase capacity and improve access time because computer applications are continually growing in size. However, there are physical limits as to how small the areas for storing information can be, as such, these memories are reaching theoretical limits in storage capacity. In addition, access tire is deteriorating as storage capacity increases. It is also desired that such computer memories have low-cost, small size and low energy consumption.
A solution to the desire for increased storage capacity, fast data transfer, and improved access time is the use of the third dimension in optical storage memories. Known three-dimensional optical storage memories have data storage densities that exceed the storage capacity of any present conventional two-dimensional optical storage memories (such as CD-ROMs) by more than three to four orders of magnitude. The increase in storage capacity stems from the ability to store information in any volume of a three-dimensional memory.
For example, the maximum theoretical storage density for a two-dimensional optical disk is 1/λ2=3.5×108 bits/cm2, while the storage density for a three-dimensional memory is 1/λ3=6.5×1012 bits/cm3, assuming that the same wavelength of light λ=532 nm is used to access the information.
Another form of high capacity optical storage medium is a three-dimensional holographic memory. Three-dimensional holographic memories also have data storage densities that exceed the storage capacity of known two-dimensional optical storage media. Experiments have been conducted on three-dimensional data storage using holographic memories made of photo-refractive materials (see D. Psaltis and F. Mok, Scientific American, November 1995, p. 52).
Although known three-dimensional memories provide improvements (e.g., access speed and storage capacity) over known two-dimensional storage memories, even these memories eventually will reach a limit in storage capacity unless a storage and retrieval process is developed which can better utilize every available volume in a three-dimensional storage memory.
Accordingly, it would be desirable to provide a data storage and retrieval system that increases the storage capacity of three-dimensional optical memories.
It would further be desirable to provide a three-dimensional optical memory that has an increased storage capacity over known optical memories.